Recent years have seen drastic improvement in joint replacement technology. Specifically hip replacement technology has improved drastically. Modern total hip replacement methods involve implantation of a femoral component. The femoral component has an intraosseous stem attached to an extraosseous neck and head. The head couples with an acetabular cup or socket, thereby forming a total hip replacement. While many designs of hip replacement provide viable solutions for ailing patients, hip dislocations, both anteriorly and posteriorly, remain a common complication. Using current designs, attempts to minimize the dislocation risk, such as by anterior displacement of the head relative to the intraosseous stem, can result in other negative outcomes, specifically leg lengthening, in-toeing gait and diminution of abductor movement.
Most femoral stems are manufactured with no built-in anterior displacement of the head relative to the intraosseous stem. Those femoral stems that provide anterior displacement of the head relative to the intraosseous stem do so by angulating the prosthetic neck in the transverse plane. Such transverse plane angulation may be accomplished with modular components or it may be accomplished by angulation to a set degree in a non-modular femoral component. However, as mentioned above, such components can result in significant negative outcomes.
In some early designs, the femoral components were angulated in the sagittal plane at the level of the intraosseous stem itself. Such designs have been abandoned because having a bent intraosseous stem makes insertion of the stem less reliable and extraction more difficult.